The present invention relates to the detection of anions in water and particularly, it relates to an apparatus for detecting anions typified by a chlorine ion, which can sense the leakage of a cooling water (seawater) of a condenser in a thermal power station and a nuclear power station.
Heretofore, in a thermal power station or a nuclear power station, as shown in FIG. 2, circulation of water is performed in such a manner that the high temperature, high pressure steam generated in a boiler 21 is led to steam turbines 23 and 25, and the steam discharged from the steam turbine 25 is condensed into water in a condenser 27 and this condensed water is again used as the boiler feedwater. Impurities such as corrosion products are accumulated in the circulation water and accordingly, a purifying apparatus (condensed water demineralizer) 29 is installed. Since the condenser 27 in this circulatory system is under reduced pressure at the steam side and uses seawater 28 as the cooling water, when a pinhole is formed in capillaries of the condenser, the seawater enters the: steam side to remarkably increase the concentration of salts. As the result, the load of the condensed water demineralizer 29 is increased, and increased amounts of leaked seawater exceed the tolerance limits of this demineralizer 29. Then, it becomes necessary to detect the seawater leakage by a salt detecting instrument.
For the detection of seawater leakage a method of measuring an electric conductivity, a sodium monitor, an atomic absorption spectrometry and the like have been employed.
The method of measuring a specific resistivity or an electric conductivity needs cation exchange resins. The reason is that in order to inhibit the corrosion in the system, ammonia and hydrazine are normally added to a circulating water in amounts so as to adjust the ammonia concentration as NH4+to about 1 ppm and the hydrazine concentration as N2H4 to about 100 ppb and the specific resistivity of the circulating water is low and the electric conductivity is high. Accordingly, the change in the electric conductivity of the circulating water by a slight increase of the salt concentration due to seawater leakage is very small, which makes it difficult to detect the seawater leakage. Here, the conventional method comprises, first, passing the circulating water through regenerative cation exchange resins to remove ammonia and hydrazine of cations which are originally present in the circulating water and cation components such as a sodium ion in the major component of NaCl having been mixed thereinto by the seawater leakage and then, measuring the specific resistivity (acid specific resistivity) or the electric conductivity mainly by HCl.
Further, the sodium monitor uses an ion-selective glass electrode and accordingly, the sensitivity in a low concentration region deviates from the Nernst equation to become lower by decrease in the electromotive force. Moreover, as a potassium chloride solution is used as the electrode solution of the reference electrode, a plus error sometimes occurs by the diffusion of a potassium ion to the sample water side. In addition, the surface of the electrode is fouled with fine particles of iron oxides and hydroxides which are called as cruds to lower the sensitivity and the like. Thus, the sodium monitor has the above described disadvantages.
With respect to the atomic absorption spectrometry and the like, at present there is no instrument for analysis of the portable type which can be set at the site and accordingly, a technique of sampling a sample water to be analyzed and bringing it to a chemical laboratory for analysis has to be taken and the circulating water cannot constantly be monitored. An instrument for ion chromatographic analysis is comparatively small but the preparation of reagents and the like take much time and moreover, the instrument is expensive as in the atomic absorption spectrometry. The method of measuring an acid electric conductivity needs cation exchange resins as described above. When a predetermined amount of ions is adsorbed on these resins, the resins cease to exhibit their adsorption capacity and need regeneration or replacement of the resins and thus, such operations and the cost of the resins become a problem.
As the apparatus for detecting anions in water which solves the above described problems, the inventors of the present invention have previously proposed an apparatus for detecting anions in water which utilizes electric continuous ion exchange equipment [Japanese Patent Publication (Kokai) JP-A-9-210943]. This equipment is provided with a chamber for dealkalization chamber which is partitioned with two cation exchange membranes between an anode chamber and a cathode chamber and filled with cation exchangers in electric continuous ion exchange equipment and an electric conductivity measuring instrument in the passage for discharging the treated water from the dealkalization chamber or provided with at least one cation exchange membrane between an anode chamber and a cathode chamber and an electric conductivity measuring instrument in the passage for discharging the treated water from the anode chamber and measures the electric conductivity of the treated water to detect the leakage of a cooling water (seawater).
The present invention relates to an improvement of this previously proposed apparatus for detecting anions in water.
Namely, the present invention relates to an apparatus for detecting anions in water with the use of an electric conductivity cell which comprises an electrolyzer constituted by an anode chamber having an anode plate and a cathode chamber having a cathode plate via a cation exchange membrane, a direct-current power unit for applying a direct-current voltage between the anode and the cathode of the electrolyzer and an electric conductivity cell for measuring the electric conductivity of a sample water, and a flow passage for introducing the sample water into the anode chamber and a treated water flow passage for discharging the treated water which has been subjected to electrolytic treatment in the anode chamber which are connected to the anode chamber of the electrolyzer, respectively, and the treated water flow passage being connected to the cathode chamber via the electric conductivity cell.
Further, the present invention relates to a method for detecting anions in water by measuring an electric conductivity which comprises introducing a sample water into the anode chamber of an electrolyzer constituted by an anode chamber having an anode plate and a cathode chamber having a cathode plate via a cation exchange membrane, applying a direct-current voltage between the anode and the cathode to effect electrolytic treatment, then withdrawing the treated water out of the anode chamber, measuring the electric conductivity of the treated water out of the anode chamber to detect anions in the water and then, introducing the treated water into the cathode chamber of the electrolyzer.